富锂正极材料xLi3NbO4·(1-x)LiMO2(M=Mn,Co;0 < x < 1)的制备及电化学性能研究

1. a 厦门大学能源学院 厦门 361005;
b 厦门大学化学化工学院 固体表面物理化学国家重点实验室 厦门 361005
• 投稿日期:2016-05-16 修回日期:2016-10-07 发布日期:2016-10-10
• 通讯作者: 龚正良,E-mail:zlgong@xmu.edu.cn;杨勇,E-mail:yyang@xmu.edu.cn E-mail:zlgong@xmu.edu.cn;yyang@xmu.edu.cn
• 基金资助:

项目受国家自然科学基金（Nos.21233004，21473148，21428303）及福建省自然科学基金（No.2014J05019）资助.

Synthesis and Electrochemical Performance of Lithium Rich Cathode Materials xLi3NbO4·(1-x)LiMO2 (M=Mn, Co; 0 < x < 1) for Li-ion Batteries

Yang Chuna, Gong Zhenglianga, Zhao Wengaoa, Yang Yonga,b

1. a College of Energy, Xiamen University, Xiamen 361005;
b State Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005
• Received:2016-05-16 Revised:2016-10-07 Published:2016-10-10
• Contact: 10.6023/A16050240 E-mail:zlgong@xmu.edu.cn;yyang@xmu.edu.cn
• Supported by:

Project supported by the National Natural Science Foundation of China (Nos. 21233004, 21473148, 21428303) and the Natural Science Foundation of Fujian Province (No. 2014J05019).

Lithium rich material xLi3NbO4·(1-x) LiMnO2 (0 < x < 1) was successfully synthesized by solid state method. Stoichiometric amounts of Li2CO3, Mn2O3 and Nb2O5 were mixed by ball milling, and the mixture was calcinated at 900℃ for 5 h under Ar atmosphere. X-ray diffraction (XRD) results indicate that the samples with 0.25 < x < 0.67 can be indexed as a cubic structure with Fm-3m space group. Electrochemical results show that the samples of x=0.25 and 0.43 have better electrochemical performance, both delivering 216 mAh·g-1 in the initial cycle between 2 V and 4.8 V. Although voltage decay is an intrinsic drawback of lithium excess materials, the sample of x=0.43 decays slower. We speculate that Li3NbO4 helps stabilizing the crystal structure. Ex-situ XPS and XAS studies show that the charging process can be divided into two stages. In the first stage, below 4.3 V, Mn3+ is oxidized to Mn4+, in the second stage, O2- is oxidized. The reversible oxidation of O2- is the origin of the achievement of large reversible capacity. Co3+ doped material 0.43Li3NbO4·0.57LiMn1-yCoyO2 (y=0.25; 0.5) was also synthesized by the same procedure. The structure of the doped material maintains the cubic structure with smaller lattice constant and the variation of lattice constant is in proportion to the amount of Co3+. Galvanostatic charge and discharge tests show that 0.43Li3NbO4·0.57LiMn0.75Co0.25O2 also delivers a large capacity of 215 mAh·g-1 in the first cycle between 2 V and 4.8 V, but the voltage plateau in the charging process decreased from 4.3 V to 4.1 V, it can be attributed to the weak dissociation energy of Mn-O bond and the overlap of Co3+/4+ 3d and O2- 2p energy band. The electrochemical impedance spectroscopy results show that a moderate amount of Co3+ doped into the material decreases the charge transfer resistance. After doped with Co3+, the rate capability is improved.